Method of rolling composite metal stock



Patented July 26, 1938 UNITED. STATES PATENTOFFICE 2,125,153 METHOD OF ROLLING COMPOSITE METAL STOCK Y 1 Thomas B. Chace, Winnctka, Ill., assignor to Clad Metals corporation of Illinois No Drawing. Application March Serial No. 131,007

23 Claims.

The present invention relates to the production of 11181011. preferably copper silicon alloy.

The specific method 01' uniting the ferrous body Although I have shown how to reduce or'elimi- 40 note these critical temperature ranges, there are certain applications of copper alloy clad steel 5 cases, the combination of temperature and time which would be injurious may, according to the present invention, be successfully avoided, and

temperature combination.

The present invention is based upon the dis- I 55 coverythat for each particular union of ferrous Industries,

Inc., Chicago, 111., a

or more of the factors of the combination. That is to say, by limiting the silicon concentration may be avoided or reduced below an objectionable value.

Given a certain analysis of the metals at the bond, the time and bond may be accurately ascertained very readily a composite metal 'ing after hot rolling of copper sion by certain reagents. W V

Since the alloying medium ofsilicon is desirable in the copper facing or the copper portion of the composite stock, and sinceits presence atthe bond appears to be'the cause of the forma-' tion of a certain crystalline structure under certain conditions be seen at once that the successful production of stock employing silicon in relatively high concentration at the bond presents a difficult problem which of the present invention to neeet.

I have found that after securing a good bond in the as bonded? state or in slab form, between the ferrousb acking metal and a silicon copper facing metal certain' practices in heating, rolling, annealing, cold rolling arenecessary to maintain a good bond in the finished rolled product. These practices are definitely related to the analyses of metals bonded or more accurately speaking; to the created at the union.

1 find that the bond at the union of the two I metals in the as bonded state is substantially inseparable, and has a tensile strength of approximately 60,000 pounds per square inch, and is actually stronger than the silicon copper'jalloy as cast. 11

Test specimens taken from such a slab usually break through the copper-alloy at some distance from the bond.

in spite of the perfect bond secured in the slab as bonded some combinations of metals will separate during initial hot rolling. Others 7 hot rolling within a show a good bond after definite temperature range, but separate easily if rolled at temperatures outside this range, par-- ticularly with cold rolling of two or more passes below the minimum of the critical temperature range. Other combinations will continue to show a good bond during hotrolling and cold rolling with intermediate anneals between cold rolling if the cumulative time and temperature of heatlimits, but willishow apoor bond if are-exceeded, g V

The diflerence in the strength of the bond before and after processing at temperatures outside the critical rangeis very apparent. For instance, a bond that "cannot be separated before processing wiil tear apart easily. after processing if that is dorfe at temperatures outsidethe critical ranges for a given analysis. 7

This change in the strength of the bonded union appears to bedue to the formation of an embrittling constituent and is probably similar to the phenomenon of precipitation hardening.

The weakened bond separ tes easily and the action onseparatiorr is very much like the breaking'up of a very hard material. A study of the conditions production of specimens subjected to inicrosco'pic examination shows that the formation of this brittle constituent is related'to a certain combination of time and temperature,

and the reduction in strength of the bond is re-.

lated; to the extent of this formation.

An exaggerated exampie of what probably takes place at the bonded section is shown by what occurs duri, the bondingfoperation when the silicon copper alloy in molten state is maintained on the ferrous slab for an excessively long period of soaking. Large irregular clusters of about one eighth of an inch in diameter are formed and suspended in the copper silicon alloy.

of time and temperature, it will it is the object tures.

are sometimes partiy visible surface of the silicon copper These formations alloy after it has solidified. These formations are very hard with a chisel,

during rolling; but are forced down through the steel backingi If the composite slab is rolled to aithin enough gauge, the formation is rolled through the steel as well as the copper and shows on both sides of the composite sheet. The section including this formation haspractically no elongation and breaks with a slight bending. Chemical-analyses of these formations show that and brittle. They cannot be cut in thickness 5 these consist mostly of insoluble iron' -and copper with a trace of silicon. tions do not occur under the same conditions with However, these forma- 15 silicon free copper, but are apparent in modified form from' longer soaking and higher tempera- Also, the formation above referred to occurs much more readily with higher silicon content in the copper.

These critical temperature ranges are definitely related to the silicon content of the copper alloy, and are, in' my opinion, the result of the of iron silicides produced at union during bonding and subsequent reheating for hot rolling and annealing. The iron from the backing material and the silicon from the facing material form the siiicides. When nickel is present either in the silicon copper alloyQor as an intermediate bonding alloy,. or in the ferrous backing metal, nickel siiicides are also formed and may have a bearing on the brittle constituent formed at the iinion. However, I have discovered that nickel definitely tends to correct for these criticai temperature ranges. Excessive iron diffusion from the backing ferrous metal into the copper of the facing alloy or insoluble iron in copper 7 soluble in copper at all temperatures and in, all proportions corrects for this, and makes a more ductile and workable alloy at the union. I

I have found that the composite metal stock composedof a high silicon copper alloy or copper alloys containing from 2% to 3.5% silicon, bonded to a ferrous backing metal are much more diflicult to roll and maintain a good bond than the lower silicon copper alloys bonded to steel such as 1.8 silicon or less. g 50 Composite slabs of these high silicon copper alloys and a ferrous metal are pretty much limited to hot rolling within the temperature range of J1,600 F. to 850 F. If the upper limit is exceeded, even for a short time and only to 1.650" F., the bond is weakened, so that the slab either separates in rolling or the finished foiled product will have a weakened bond which can be pulled range will not cold roll to any extent even after annealing without separating at the bond. Gold is limited to about ten three cold rolling after annealing per cent reductions and to two'v or passes.

Composite copper galloys oi less than stcck comprising the lower silicon "0 two 'per cent silicon bonded to steel are much less sensitive to time and temperature 7. in fact,

in hot or cold rolling practice; these combinations are not subject to the minimum hot rolling temperature. They 75 F. and

same sheet of 1.34

can be hot rolled froIii a higher maximum temperature of near 1,700 F and passed without regard for minimum temperaturauntil the material hardens to the extent that further reduction is impractical and no injurious effect on the bond is apparent. This material can also be reheated numerous times for hot rolling or annealed and cold rolledto any extent that the mill can reduce it in thickness without any apparent weakening of the bond. For instance, the material has been cold rolled after annealing to better than 70 per cent reduction without any noticeable effect on the strength of the bond. However, I find that all heating of the composite stock within the temperature range of l,l50 F. to 1.700 F. tends to form the embrittling constituent at the union which if formed to excess is very destructive to the bond strength, and if care is not taken. to avoid certain practices or combinations of time and temperature within this range that this compound is created at the union to the extent that the two metals will separate in rolling or can be pulled apart after rolling. The intermediate temperature range near 1,400*F. is particularly destructive and I believe that in this range of approximately 1,350 F. to 1.450 F. that precipitation of the elements forming the brittle bond is much'more rapid than in the lower range of approximately 1,150 F. to

The higher temperature range of 1,500 to F. apparently tends to redissolve the embrittling compounds and maintain them in solid solution. For example, samples taken from the per cent silicon copper clad steel after hot rolling from the bonded slab showed perfect inseparable bond. One of these specimens was annealed for one hour at 1,425 after cold rolling the copper alloy and steel separated easily. Other specimens from this same sheet heated for one hour at 1,550 F.

, and at 1,200" F. and cold rolled showed good bond.

However, heating for longer periods of one and one-half hours and two hours at 1,550 F. showed failure at the bond, whereas the longer periods at 1.200 Fywere not injurious. Shorter periods at the .most critical temperatureof 1,425 F. were not so destructive so than at 1,550 or 1,200 F. It is therefore obvious that this particular temperature range of 1,350 F.-l,450 F. should be avoided as much as possible. Also the total time and temperature of heating for hot rolling and annealing for cold rolling is important, and that a practice must be established depending on the analysis and size of the slab to successfully convert the cast composite slab into finished rolled products. The soaking period for all heats in the furnace after the material has reached temperature should be held to a minimum and in allcases only sufficient to soften the metal without undue precipitation of the elements during total heating so that the formation of the brittle compound is held to a minimum and insufficient to cause brittle bond.

Generally, the preferred practice for treating steel clad with a silicon copper alloy of 1% to 2% silicon is to heat for hot rolling in, the range of 1.500 F. to 1,700 E, and hot roll until material hardens to the extent that further reduction is not practical, reheat within same range for subsequent hot rolling, taking care to limit the soaking period at maximum tempera.- ture to approximately fifteen minutes; anneal for cold rolling within the range of 1,100 F.

but appreciably more 3 1,350 F. The higher the annealing temperature. the shorter should be the soaking period after metal has reached temperature. The initial anneal after hot rolling can be at the maximum of this range or 1,350 but the length of time in the furnace -after the metal is soaked through should be limited to twenty minutes. Subsequent anneals between cold rolling should be at the lower part of the range of 1,100 to 1,350 F. At 1,200 F., one and one-half hours soaking has been found satisfactory and at 1,100 F. up to two hours soaking hasnot produced a brittle bond. The exact detail of the heating or annealing practice is dependent on the original thickness of the composite slab, the number of ann'eals necessary or the extent of totalreduction to finished gauge, and if a great many anneals are, scheduled to reduce the material to finished gauge, then care should be taken to work to the minimum time and temperature combinations, so that the accumulation is still within the maximum limits.

For instance, the detail of the preferred practice for-rolling composite material composed of a ferrous backing metal and a silicon copper alloy, which forms an analysis at the copper alloy side of the bond union of approximately 1.4 per cent silicon, .65 per cent nickel, 0.8 per cent iron, 0.2 per cent manganese with small amount of carbon is, heat in a furnace to 1,550" F. until the slab is heated through and limit soaking to twenty minutes after saturation; hot roll until material hardens to the extent that further reduction is not practical; reheat within same practice for subsequent hot rolling; anneal initially at 1,325" F. for not more than forty-five minutes after metal has reached temperature; cold roll to any extent that is practical for the rolling mill; reanneal after cold rolling at 1,175 F. for not more than two hours after reaching temperature; repeat this for intermediate anneals between additional cold rolling.

If heating for hot rolling is limited to three heatings for not more than heat after metal has reached temperature, annealing for cold rolling at 1,550 F. is satisfactory, but soaking time should be limited to ten minutes per heat after metal is heated through.

The silicon copper alloys may contain from 0.1 per cent to 3.5 per cent silicon and such'other elements as nickel, for facilitating bonding, and nickel and iron for increasing the compression resistance of the copper alloy or small amounts of manganese, zinc, tin, aluminum' or phosphorous to generally improve the alloy. The ferrous base metal may be any of the carbon steels, low alloy steels or high alloy steels, such as highnickel steels.

I do not intend to be limited to the precise ranges of time or temperature above disclosed. except as the same are specifically recited in the appended claims.

I claim:-

1. Method of working, such as rolling, a composite-metal stock comprising a 0.1% to 3.5% silicon copper alloy and a ferrous alloy which includes heating the metal for hot rolling or annealing the metal for cold rolling sufiiciently to soften the metal but without causing the formation of a brittle constituent at the union of the two metals; 5

2. Method of working, such as by rolling, an inseparable slab of a,-0.l% to 3.5% silicon copper alloy bonded to a ferrous alloy which includes fifteen minutes perthe method of heating the slab for hot rolling 76 and annealing the slab for cold rolling. whereby the bond is maintained in inseparable state in the finished rolled product.

3. Method of reducing the thickness and increasing the area of a composite metal stock comprising a 2% to 3 /2% silicon copper alloy bonded to a ferrous alloy which includes heating the slab to a maximum temperature of 1.650 F. and hot rolling until the slab has reached a minimum temperature of 850 F.

4. Method of claim 3further characterized by the presence of nickel in the copper alloy in amounts less than-the silicon content.

5. The method of claim 3 wherein the silicon copper alloy is characterized by the presence of iron in thecopper alloy in the amount of less than 3%.

'6. The method of reducing the thickness and increasing the area of composite metal stock comprising a silicon copper alloy of 2% or less silicon bonded to a ferrous alloy which includes heating the slab to a maximum temperature of 1,700? F. and hot rolling without regard for minimum temperature.

7. The method of'claim 6 further, characterized by the silicon copper alloy being initially bonded to the steel by fusion of the silicon copper alloy. 8."I'he method of reducing the thickness and increasing thearea of a composite metal slab 30 comprising a silicon copper alloy of less than 2% silicon bonded to a ferrous backing metal which includes heating the slab between 1,500 F. and 1,700 F., hot rolling without regard for minimum temperature, annealing at temperatures between 1,100 F. and 1,300 F., and cold rolling.

9. Method of claim 8 further characterized by the presence of nickel in the copper alloy in amounts less than the silicon content.

10. The method of reducing the thicknessand increasing the area of a composite metal slab comprising a silicon copper alloy of less than 2% silicon, bonded to a ferrous backing which inchides heating the slab between 1,500

tween 1',500 F. and 1,700 F., and cold rolling with subsequent intermediate ann'eals between cold rollings in a temperature range of 1,100 F. and 1,300 E. 1

11. The method of claim 10 further characterso ized by the presenceof nickel in amounts less than the silicon content, iron in amounts .less ..han 3%, and manganese of approximately in the copper alloy. 12. The method of reducing the thickness and increasing the area of composite metal stock thantwo hours after saturation for additional anneals between cold rolling.

13. The method of claim 12 wherein the ferrous alloy is a nickel steel and at least part of the subjected and the time .to a value below that at which injurious crystal- F. and 1,700 F., and hot rolling-annealing initially beperature of substantially 1,550 substantially 20 minutes.

comprising a copper alloy of approximately 1.4%

nickel content and iron content of the copper alloy is diffused from the nickel iron alloy.

14. Method of treating composite metal stock consisting of a ferrous backing .and a 0.1% to 3.5% silicon copper alloy by fusion of the alloys which comprises heating the stock to a temperature which will soften the same suitable for rolling and limiting the time during which such temperature is maintained to less than that in which embrittler'nent of the bond between backing and facing occurs, and then rolling the stock to reduce the section.

15. Method of preventing injurious crystallization at the fusion bond between a ferrous backing and a 0.1% to 3.5% silicon copper alloy facing during processing which comprises limiting the product of the temperature to which the bond is during which it is heated lization will occur.

16. Method of maintaining a tenacious bond between a ferrous backing and a 0.1%to 3.5% silicon copper alloy facing during the process of rolling which comprises maintaining the product of time and temperature below that value which is required for the formation of a brittle crystalline structure at the meeting faces of the backing and facing.

17. Method of 'maintaining in a composite metal body a tenacious bond formed by'fusion between a ferrous backing-and a 0.1% to 3.5% silicon copper alloy which comprises heating the body to a temperature and for a time less than that required to form crystal silicides at the meeting faces of the backing and facing.

'18. Method of reducing by rolling a composite slab consisting of a ferrous backing and a 0.1% to 3.5% silicon copper facing with the presence of nickel at the bond, which comprises heating the slab to a temperature of substantially 1,550 F.

and hot rolling to reduce the thickness of the slab until the metal hardens.

19. Method of claim 18 further characterized by limiting the soaking while heating to said tem- F. to a period of 20. Method 'of claim 18 further characterized by reheating for further hot rolling again to substantially' 1,550 F. and limiting 20 minutes.

21.. Method of claim 18'further characterized by annealing before coldrolling by heating to substantially 1,325 F. and then cold rolling.

the soaking to 22. Method of claim 18 further characterized.

by annealing before cold rolling by heating to substantially 1,325 F. and then cold rolling, and subsequently reannealing at substantially 1,175 F. for not more than temperature for further cold rolling.

23. Method of claim-18 further characterized by limiting the heating for either hot rolling or for annealing prior to cold rolling to a combination of time and temperature which will be less than that required for the formation of an injurious crystalline structure at the bond.

facing bonded thereto two hours after reaching THOMAS B. CHACE. 

